Further Characterization of the Red Beet Plasma Membrane Ca²⁺-ATPase Using GTP as an Alternative Substrate

Abstract

The GTP-driven component of Ca2+ uptake in red beet (Beta vulgaris L.) plasma membrane vesicles was further characterized to confirm its association with the plasma membrane Ca2+-trans-

A Single Gene May Encode Differentially Localized Ca2+-ATPases in Tomato.

“…These data are consistent with the lack of a calmodulin binding domain in the deduced LCA amino acid sequence (Wimmers et al, 1992). In previous studies, calmodulin sensitivity was reported for the PM Ca2+-ATPases from maize (Robinson et al, 1988;Briars and Evans, 1989), red beet roots (Williams et al, 1990), carrot cell cultures (Hsieh et al, 1991), and radish seedlings (Rasi-Caldogno et al, 1992. In contrast, calmodulin had no effect on the PM Ca2+-ATPases from pea roots (Butcher and Evans, 1987) and Commelina communis leaves (Siebers et al, 1990).…”

Identification of the Plasma Membrane Ca2+-ATPase and of Its Autoinhibitory Domain

“…Vol. 108, 1995 fairly similar biochemical characteristics and their reported values of molecular mass fall in the same range (Evans et al, 1989;Williams et al, 1990;Hsieh et al, 1991;Askrdund andEvans, 1992, 1993;Chen et al, 1993;Thomson et al, 1993Thomson et al, , 1994; therefore, they are not easily discerned.…”

“…In fact, it is half-saturated by Ca2+ in the micromolar range and has a very high affinity for MgATP (Rasi-Caldogno et al, 1989;Carnelli et al, 1992;De Michelis et al, 1992. Finally, the PM Ca2+-ATPase activity is regulated by CaM, which strongly increases the V,,, of the reaction, thus making the enzyme up-regulated by an increase of cytosolic Ca2+ and Ca2+-CaM concentrations (Malatialy et al, 1988;Robinson et al, 1988;Williams et al, 1990;Erdei and Matsumoto, 1991;Carnelli et al, 1992;Rasi-Caldogno et al, 1992;De Michelis et al, 1993).…”

“…In fact, the PM Ca2+-ATPase has a very high affinity for CaM; therefore, its stimulation by exogenous CaM is often very slight or even undetectable unless endogenous CaM is stripped by drastic treatments with Ca2+-chelating agents (Williams et al, 1990;Rasi-Caldogno et al, 1993a). Moreover, a CaMstimulated Ca2+-ATPase is present also in endomembranes such as ER and tonoplast (Malatialy et al, 1988;Brauer et al, 1990;Hsieh et al, 1991;Askerlund and Evans, 1992;Chen et al, 1993;Gavin et al, 1993;Gilroy and Jones, 1993) and it has been proposed that the bulk of CaM-stimulated Ca2+-ATPase is localized at endomembranes (Askerlund and Evans, 1992).…”

“…Identification of the PM Ca2+-ATPase lon gel electrophoresis has been accomplished up to now by utilizing the characteristic of the enzyme to form a phosphorylated intermediate during the catalytic process (Williams et al, 1990;Askerlund and Evans, 1993;Thomson et al, 1993). In this work, to study the effect of controlled proteolysis on the PM Ca2+-ATPase at the molecular le\rel, besides following the migration of its phosphorylated intermediate in acidic gels, we have developed methods suitable also for SDS-PAGE according to Laemmli (1970), exploiting some characteristics of the enzyme.…”